1. Field of the Invention
The present invention relates to electrical connectors and more specifically, the present invention relates to an edge mount mezzanine array connector and an edge mount backplane array connector.
2. Description of the Related Art
Electrical connectors are used to place electrical devices, such as printed circuit boards, in communication with one another. An electrical connector may be thought of as having two portions, one portion of which connects to a first electrical device and the second portion of which connects to a second electrical device to be put into communication with the first device. To connect the two devices, the two portions of the electrical connector are mated together.
Each portion of the connector includes one set of contacts or terminals adapted to communicatively couple to an electronic device and a second set of contacts or terminals adapted to matingly couple to the other connector portion. This can be readily accomplished by designating one portion of the connector as having “male” contacts or terminals adapted to couple to the other connector portion's “female” contacts or terminals. Regardless of the specifics of the design of the contacts or terminals, the two connector portions should be adapted to be easily connected and disconnected from each other to respectively electrically link and unlink the electrical devices to which they are connected.
Accordingly, each connector portion is fixedly connected to an electronic device through its remaining set of contacts or terminals. The contacts or terminals may be removably or permanently connectable to the electrical device; however, it is usually desired that the connector portion be secured to the electrical device through some physical mechanism. Typically, the connector portions are secured to electrical devices by fusing the contacts or terminals to contact pads or the like formed on the electrical device.
Recently, there has been a trend toward miniaturization of most electrical devices. As electrical devices become smaller and more complex, the electrical connectors used with these devices must also become smaller and must be able to accommodate the more complex devices. One problem with miniaturized electrical connectors arises from the increased precision of placement necessary to produce the proper positioning and connection of the connector contacts or terminals onto the device. This problem is exacerbated by the ever-increasing input/output (I/O) density requirements demanded of the progressively smaller electrical connectors by increasingly miniaturized electrical devices. With increased pin counts (e.g., greater number of terminals) in each connector, it becomes more and more difficult to maintain desired levels of co-planarity while maintaining contact of all of the terminals to a substrate or PCB.
One means of addressing the need for increased I/O density is to provide an array connector. Such an array connector can provide a high-density two-dimensional array of contacts or terminals for interfacing with an electrical device. However, array connectors present attachment difficulties regarding connection to devices (i.e., circuit boards or substrates) since most of the contacts or terminals must necessarily be positioned in the interior of the two-dimensional array area and are accordingly difficult to align upon connection, visually inspect, and/or repair.
Other types of connectors are also known and used for connection to a printed circuit board (PCB). For example, “board edge” connectors or “straddle mount” connectors, which are straddle-mounted to an edge of a PCB and has a common ground member for rows of signal conductors installed inside of the connectors to connect with the pads disposed on or both sides of the PCB, are known. See, for example, U.S. Pat. Nos. 5,472,349; 6,231,355; 6,692,273; and 6,688,897.
For such connectors, through-hole mounting technology has been used. Mounting portions of the terminals are placed in through holes of the PCB and held in place by soldering or some type of mechanical engagement of the pin with sidewalls of the through hole. As the need for high density of the connector increased, the number of through holes required also increased. However, since the diameter of the through holes is relatively large, only a limited number of through holes could be provided in a given area. Therefore, through-hole technology could not meet the requirement for high density applications. In addition these through holes negatively affect the electrical performance of the connector.
In order to provide for a higher density of connectors on the board, surface mount technology has been utilized. Examples of surface mount connectors can be found in U.S. Pat. Nos. 5,813,871 and 5,860,814. Because no through holes are required, conductive pads on the printed circuit board can be closely spaced, thereby allowing a connector with condensed terminals to be mounted in an area of the board which would be impossible for a through-hole version.
As the progression toward higher density continues, it has become imperative that every possible area of the printed circuit board be effectively utilized. A straddle mount connector located on an edge of the printed circuit board was then developed to occupy a minimal board area. Additionally, with the trend of high-speed signal transmission, vertical straddle mount connectors and right angle connectors generally use a ground bus to provide a ground reference to signal contacts for improved signal integrity at higher speeds.
The solder tails of the straddle mount connector wipe the solder paste off of the pads of the printed circuit board when the connector is assembled with the printed circuit board (see, for example, FIG. 1 of U.S. Pat. No. 6,692,273). The solder tails on the straddle mount connector need to be forgiving enough to accept the large tolerance range of the printed circuit board thickness. That is, if the solder tail gap is too large and the printed circuit board is too small, then proper soldering will not occur. Further, in many cases the forces associated with mating and unmating the straddle mount connector are directly transferred to the solder joints on the printed circuit board, which can result in fractured solder joints.
It is also known to use a right angle connector, as shown in FIG. 12. This type of right angle surface mount connector can be used for an array connector or a backplane connector. As is seen in FIG. 12, a PCB 600 must have a plurality of holes 610 formed therein to accommodate tails 652a of the contacts 652 of the right angle connector 650.
The tails 652a of the contacts 652 are typically compliant pins that provide electrical connections to the printed circuit board 600. The compliant pins 652a in right angle backplane connectors adversely affect signal integrity because they require the large diameter plated thru holes 610 to be formed in the printed circuit board. These large plated thru holes 610 require large anti pads to be placed in the ground planes of the printed circuit board, which also adversely affect the signal integrity.
When the compliant pins 652a are inserted into the plated thru holes 610, many problems may occur. In many cases, non-symmetrical forces associated with mating and unmating the right angle surface mount connector 650. Further, the right angle surface mount connector sits on just one side of the printed circuit board so that the mating and unmating forces are offset from the centerline of the thickness of the PCB, causing them to be non-symmetrical.
Coplanarity of the SMT solder tails on a high density right angle surface mount connector can be very difficult to control, which results in improper soldering of the right angle surface mount connector. The right angle surface mount connector's weight distribution will cause the connector to sit incorrectly on the PCB during the soldering process, which will cause improper soldering. Also, in many cases, non-symmetrical forces associated with mating and unmating the right angle surface mount connector 650 are directly transferred to the solder joints on the printed circuit board which can result in fractured solder joints.
As can be determined from FIG. 12 (and FIG. 1 of U.S. Pat. No. 6,652,318), when the right angle connector is assembled to the PCB, significant forces are required to insert the compliant pins 652 into the plated holes 610, and the other ends 652b of the contacts 652 must be attached to another PCB or electrical device as seen FIG. 1 of U.S. Pat. No. 6,652,318, which causes non-symmetric forces.
Furthermore, up until this time, it has always been required that the ends 652a of the terminals 652 of a full density right angle connector be routed to a single side of a PCB, such as PCB 600.